The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPPthird generation partnership projectEARFCNEUTRA absolute radio frequency channel numberEUTRAevolved universal terrestrial radio accessIEinformation elementLTElong term evolution (EUTRA network)LTE-ALTE-advancedRANradio access networkRFradio frequencySIsystem informationSIBsystem information blockUARFCNUTRA absolute radio frequency channel numberUMTSuniversal mobile telecommunication systemUEuser equipment
Cellular radio communications now include individual cells operating on multiple radio frequency channels in order to better support a variety of different UEs, some of which may be capable of operating on only one of these frequency bands which is different from a band for which another UE in the cell is capable. Additionally, some bands in use by one cell may have some frequency portion overlapping with bands in an adjacent neighbor cell, particularly where such neighbor cells operate under different radio access technologies, such as for example UMTS and LTE. For example, in the HSPA version of UMTS, bands II and XXV have respective frequency bands 1930-1990 MHz and 1930-1995 MHz and thus are overlapping in frequency. There is a similar overlap among bands V (869-894 MHz), VI (875-885 MHz) and new band XXVI (814-849 and 859-894 MHz); bands IV (2110-2115 MHz) and X (2110-2170 MHz); and bands III (1805-1880 MHz) and IX (1844.9-1879.9 MHz).
Relevant to the above scenarios are certain proposals for LTE Release 10 set forth in document R2-114158 by Qualcomm entitled “Multiple harmonised bands per cell” and in document R2-114299 by Ericsson and ST-Ericsson entitled “Multiple frequency band indicators in a cell” (both from 3GPP TSG-RAN WG2 meeting #75; Athens, Greece; 22-26 Aug. 2011). Specifically, these documents propose that some cells which belong to a frequency in an overlapping band will broadcast the multiple bands they support according to variously named extension fields for the SIB1. In the examples given, these are in the context of a new band 26 which was recently introduced into Release 10 discussions. This broadcast that multiple bands are supported is to allow new UEs which support the new band 26 to relax their RF requirements as compared to the older defined bands so that, when roaming onto an operator's band, they may then apply the new relaxed requirements, and thereby avoid the UE having to perform interoperability testing (IOT). These proposals are to additionally allow older UEs supporting the older bands to camp on the same cell as well as to allow legacy UEs to camp on the newer band. These proposals seek to adapt the requirement at section 5.4 of 3GPP TS 25.101 v10.2.0 (2011-06) that a cell is allowed to indicate in SI only one frequency band that it supports.
A problem arises in the above solutions when considering UE mobility between cells. A UE performs mobility based on a neighbor list given to it by SI. The conventional practice is that for UMTS, the individual cells on each frequency are listed, and for LTE only the frequency is listed. But if the above proposals of introducing multiple bands support in a cell were adopted, the UE would not know whether the neighbor cell (UMTS) or neighbor frequency (LTE) belongs to a frequency band which the UE supports until after that UE reads SI from the target cell (specifically, SIB5 if the target cell is UMTS and SIB1 if the target cell is LTE). So in some cases the UE will give up on re-selecting to the neighbor cell because of a non-supported frequency band only after the UE performed some mobility related processes (such as neighbor cell measurement, cell quality evaluation, cell reselection, target cell SI reading), which depletes the battery or other portable power source of the UE. Since the UARFCN (UTRA absolute radio frequency channel number) or EARFCN (EUTRA absolute radio frequency channel number) indicated in the neighbor cell/frequency list may belong to multiple bands, the UE cannot determine which band to which it refers.
Further, the serving cell's broadcast of its own UARFCN/EARFCN referring to a specific frequency can be different for a different band; different UARFCN/EARFCN can refer to the same frequency but in a different band/channel. In this case, the neighbor cell/frequency list which the UE uses for mobility purposes would need to be updated to broadcast the same frequency multiple times so that all UEs can reselect. But this then causes a problem in that there is a limited number of cells which can be broadcast in the UTRAN neighbor cell list. Even in some of today's networks, the size limitation imposed by the signalling restrictions of the UTRAN neighbor cell list can restrict the neighbor cell configuration and therefore increasing the size further is not practical. This also causes a problem due to there being a maximum number of frequencies in UTRAN and/or EUTRAN which the UE which is required to measure. In UMTS, the UE is required to be able to measure two frequencies in addition to the carrier (serving cell) frequency, and in LTE the UE is required to measure three frequencies in addition to the carrier frequency. If for example the serving cell supports three bands, the neighbor cell/frequency list size may increase by a factor of three. In principle, the UE could measure three bands if the frequencies are all identical, but this is not required by current radio specifications because currently there is no possibility for a cell to belong to more than one band.
For that reason, this issue was not a concern in the past. While there were some overlapping frequency bands (for example, Band V and Band VI overlap), there was no practical situation that the Band V cell could be signalled as a neighbor cell of a Band VI serving cell and additionally there was no possibility for either the serving or neighbor cell to support multiple bands. The detailed teachings below resolve the above problem which is wasteful of the UE's limited power source.